This invention relates generally to the field of medical devices, and particularly to a method and apparatus for forming a catheter balloon in which balloon material is removed from an inner surface of the balloon.
Medical balloon catheters, particularly those configured for use in the peripheral vasculature anatomy, desirably have relatively large working balloon diameters coupled with relatively small diameter catheter shafts. Details of angioplasty and peripheral vasculature balloon catheter design can be found in U.S. Pat. Nos. 5,042,985 and 5,061,273, incorporated herein by reference in their entireties. A conventional technique for fabricating catheter balloons involves blow molding a parison. The parison, or balloon tubing, must have sufficient wall thickness to provide enough material to allow expansion of the parison to the working diameter of the balloon during the blow molding operation. Furthermore, the diameter of the parison must be compatible with the shaft diameter of the catheter to which the balloon will be attached. A parison is prepared, as for example by extruding tubing having wall thickness sufficient to provide material for blowing the balloon. Typically, the proximal and distal sections of the tubing are necked to reduce the diameter to be compatible with the desired catheter shaft, using a hot die and a mandrel. The outer diameter of the necked tube is controlled by the diameter of the die, while the native wall thickness of the tubing generally limits the size of the mandrel that may be used, and thus, the resulting inner diameter. Prior art techniques have difficulty generating satisfactory parisons for a relatively large diameter balloon configured for use with a relatively small diameter catheter shaft. The diameter of the proximal and distal portions of the parison is dictated by the diameter of the catheter shaft. When preparing parisons for a larger diameter balloon, the greater wall thickness required for blowing the balloon necessitates the use of a smaller mandrel. This can result in an undesirably small inner diameter in the proximal and distal portions of the parison that are not expanded or expanded very little during the blow molding operation.
Accordingly, there is a need for methods of forming balloons for catheters that couple a relatively large diameter balloon with a relatively small diameter catheter shaft. There is a further need for balloon forming methods that provide a relatively large diameter balloon with a relatively small diameter catheter shaft that still have sufficient inner diameters. Additionally, there is a need for such balloon fabrication techniques that are cost effective, improve reliability and are compatible with conventional blow molding methods. This invention satisfies these and other needs.
The invention is inflatable members for catheters, and a method of forming such inflatable members, generally comprising providing an inflatable member with a section having an inner diameter, and enlarging the inner diameter of the section of the inflatable member. In a presently preferred embodiment, the section to be enlarged is a generally noninflatable shaft section of the balloon. A presently preferred embodiment comprises placing at least a section of the inflatable member in a mold, inflating the section of the inflatable member to conform the inflatable member to the interior surface of the mold, and removing material from the inner surface of the inflatable member, such as for example, an inner surface of the proximal shaft section and/or distal shaft section of the inflatable member. Preferably, the step of enlarging the inner diameter of the shaft section of the inflatable member comprises removing material from the inner surface of the shaft section, as for example by abrading, machining or drilling. The balloon may be formed by a variety of suitable methods such as blow molding in a first balloon mold, and then put into a second mold of an assembly for removing material from the shaft section to thin the shaft section wall.
The invention also includes devices for enlarging the inner diameter of a section of an inflatable member, generally comprising a mold configured to cover at least a section of the inflatable member and a drill at one end of the mold. A presently preferred embodiment comprises a fixture secured to a mold, the mold having an inner dimension corresponding to the outer dimension of the inflated inflatable member, a drill centered axially with the mold, and a fitting for introducing pressurized air into the inflatable member. The mold may encompass the entire length or less than the entire length of the inflatable member. The pressurized air blows cutting debris away from the balloon, and displaces the central working length of the balloon radially away from the path of the drill, both of which would otherwise damage the balloon wall.
The method and apparatus of the invention provides a catheter balloon having an enlarged inner diameter shaft section, without damaging the balloon during enlargement of the shaft inner diameter, and may be used to prepare a balloon with a large working diameter and a desired shaft section diameter. These and other advantages will become more apparent from the following exemplary figures and detailed description.